1. Field of the Invention
The present invention relates to a sheet feeder for feeding printed sheets to a conveying device. The sheet feeder has a gripper drum with at least one gripper for removing the printed sheets one at a time from a stack; a pocket, which is permanently mounted essentially in the peripheral area of the gripper drum and in which the printed sheets can be aligned against a stop with the fold forward and set down on the conveying device with reversal of direction; and a decelerating device, which slows the speed of the printed sheets downstream towards the stop.
2. Description of the Related Art
Sheet feeders of this type are known especially as signature feeders of gathering and stitching machines. These have a gripper drum, with which printed sheets in a stack are tipped at a front edge, gripped and guided one at a time to stops, also known as register stops, on which the printed sheets are aligned. During this process, the sheets are held in the peripheral area of the drum by guides, which form a pocket and are mounted in a stationary way. The printed sheets are pulled from this pocket one at a time by their rear edges and opened with opening drums. They are then set down in roof-like fashion on a gathering line.
The printed sheets are often provided with an overlay fold to allow them to be opened. The different length of the front side and rear side of the folded printed sheets thus allows central opening. During the further processing of the gathered printed sheets, these overlay folds must be cut off in a cutting device to realize a clean appearance of the printed products. The overlay fold thus serves only for correct processing of the printed sheets and ultimately winds up as waste, which, of course, must be kept low. Conflicting with this goal is the fact that in a high-speed sheet feeder, the printed sheets strike at high speed in the pocket and do not have time to stabilize in this position. Especially the end of the printed sheet that is located in the pocket thus lies unsteadily and inexactly, which makes it more difficult to realize reliable gripping and opening with the smaller overlay fold that is desired. Therefore, in high-capacity sheet feeders, the overlay fold must be made longer than would be desirable from the standpoint of waste production.
To stabilize the printed sheets in the pocket, the sheet feeder disclosed by EP 0 716 995 A has a pocket with a rubber stop, which is meant to dampen the impact of the printed sheets. In the sheet feeder described by DE 197 38 920 A, an endless belt is provided, which is intended to stabilize the printed sheets in the pocket with frictional contact.